Proving: 3A = (cos(2A)-cos(4A))/(sin(4A)-sin(2A))

[LoveandHate]

Homework Statement

I have to prove that 3A=(cos(2A)-cos(4A))/(sin(4A)-sin(2A))

Homework Equations

All of the trig identites.

The Attempt at a Solution

Well, I know I can expand tan(3A) to sin(3A)/cos(3A). After this, I have no idea what to do. I do not know any way to simplify or expand the right side of the equation. If someone can help me out by just showing the me the first step, if possible, then I can try to solve the rest of the identity by myself.
Thanks!

 

[Mark44]

Homework Statement

I have to prove that 3A=(cos(2A)-cos(4A))/(sin(4A)-sin(2A))

Homework Equations

All of the trig identites.

The Attempt at a Solution

Well, I know I can expand tan(3A) to sin(3A)/cos(3A). After this, I have no idea what to do. I do not know any way to simplify or expand the right side of the equation. If someone can help me out by just showing the me the first step, if possible, then I can try to solve the rest of the identity by myself.
Thanks!

I don't think you have written the problem correctly. I believe you meant to write
tan(3A) = (cos(2A)-cos(4A))/(sin(4A)-sin(2A))

If so, start with the right side and notice that 2A = 3A - A, and 4A = 3A + A.